It should be now possible to define which genetic and other alterations, or combinations there of, can be interpreted as reliable biomarkers of exposures. By identifying changes associated with tumor cells and surrogate tissues associated with specific known and suspected environmental risk factors, it may be possible to identify particularly high-risk individuals and potentially design an efficient strategy for cancer prevention. Cancer' is therefore a generic term used to describe a group of at least a hundred diseases that occur when malignant forms of abnormal cell growth develop in one or more body organs. Cancer arises after a series of genetic mutations remove the normal checks on cell growth. These cancer cells continue to divide and grow to produce tumours. Cancer cells can invade adjacent structures and spread via the lymph or blood to distant organs. Some of the biological mechanisms that change a normal cell into a cancer cell are known while others are not yet known. Cancer differs from most other diseases in that it can develop at any stage in life and in any body organ. No two cancer cases behave exactly alike. Some may follow an aggressive course, with the cancer growing rapidly. Other types grow slowly or may remain dormant for years. Very high cure rates can be achieved for some types of cancers, but for others the cure rates are disappointingly low and await improved methods of detection and treatment. The wide range of cancer treatments and associated services reflects the biological diversity of cancer. The most common stage of cancer at diagnosis, the rate of progression, and the treatment options vary significantly with the type of cancer a patient presents. It is estimated that about 80% of cancers are due to environment or lifestyle, and therefore are potentially preventable.